In order to mark or delineate for visibility at night time by vehicle drivers road side edge portions (or road side edge barriers, or road median strips delineating the space interval between two adjacent highway surfaces running parallelly to one another, or curved exit or entrance ramps associated with so-called super highways and other roadways, or tunnels, or bridge structures, or any hazardous object along a road), vertically oriented reflectors have been employed. In general, three types of prior art reflectors have been employed for this type or class of application: (1) the prismatic triple mirror type reflector using a plurality of standard reflex type units wherein the individual cube axes are perpendicular to the surface of the reflector; (2) the glass bead-type reflector sheeting wherein glass beads are embedded thereinto; and (3) the prismatic triple mirror type reflector using a plurality of angled cube corner-type retroreflective units, such as a reflector adapted from the teachings of Heenan U.S. Pat. No. 3,332,327 which is normally mounted horizontally on the pavement as a center line marker or the like, but which, in this application, is mounted vertically and which here utilizes only the front ramp-like surface of such reflector body. In this class of application, the performance of all three of these reflectors is similar to one another in that the peak of retroreflectivity of each type in terms of light intensity when such is so mounted upon a road side edge or the like in a vertical orientation is parallel to a tangent to the road at that point. Retroreflectivity extends from that parallel position (sometimes termed 0.degree.), or from such a peak intensity location, through typically angles up to about 25.degree. to 30.degree. into the roadway, although the glass bead-type reflector sheeting appears to have slightly more angular range than this, going up to perhaps about 40.degree..
In all known such prior art types of reflectors adapted for this class of application, the reflected light output, or performance of retroreflectivity, decreases with increasing angles to such tangent to the road. This decrease is such that, as a car moves down a roadway at night, for example, the driver has each individual road side reflector in view (as respects retroreflected light) only through a maximum angle typically not greater than about 30.degree.. For the rest of the time interval that the driver is before, approaching and passing an individual reflector (which thus covers an angular range or zone of from about 30.degree. to 90.degree.), the driver is unable to see the individual reflector by retroreflected light because such reflector is not retroreflective of the car headlights in that zone. Perhaps the driver can physically see an individual such reflector, but once the driver is beyond 30.degree., and in the range of from 30.degree. to 90.degree., he can not see or receive any retroreflected light signal therefrom.
There is a need for an improved roadside reflector means which will permit the drivers of vehicles to see individual roadside reflectors for a considerable distance along a road ahead. Such retroreflective viewability could be achieved by using individual reflector means each of whose retroreflectivity characteristics continuously extends at least from about 0.degree. up to at least about 60.degree. and which reflectors are stationed at spaced intervals along road side edge portions.
So far as is known, nothing in the prior art in any way teaches or suggests roadway edge marking reflector means adapted to provide appreciable, or practically sufficient, retroreflectivity beyond about 30.degree. so that continuous retroreflectivity over zone of from about 30.degree. to 60.degree. is actually completely unachievable by prior art roadside reflector systems. Between about 30.degree. and 40.degree., some retroreflectivity is possibly provided by glass beaded reflectors (for example, a glass beaded sheet the so-called "Scotch-Light" type (trademark) available from Minnesota Mining & Manufacturing Company, St. Paul, Minn.), but the 10.degree. wide zone from 30.degree. to 40.degree. is found to be only weakly retroreflective for such glass beaded sheeting, so that the viewability and the retroreflectivity characteristics of glass beaded sheeting is generally considered by those skilled in the art of highway barrier marking to be insufficient for adequate highway safety practices at these angles of from 30.degree. to 40.degree.. Currently, glass beaded reflectors are accepted as a 0.degree. to about 25.degree. material, and very little use is made of the retroreflectivity characteristics of glass beads in the range of from about 25.degree. to 40.degree. because of this inherent weakness.
While, as indicated, no known individual reflector constructions adapted for this desired class of application have continuous retroreflective viewability characteristics over such ranges (relative to a road), cube corner type retroreflector constructions having retroreflective continuous viewability characteristics over a range of from about 0.degree. to 70.degree. (measured in the same relative direction as that herein used in reference to the present class of application) have heretofore been known to the prior art, but have been employed in, and constructed for, use in other fields of application. For examples, see Heenan et al U.S. Pat. No. 3,887,268, Heenan et al U.S. Pat. No. 3,541,606; Golden et al U.S. Pat. No. 3,887,268, Nagel U.S. Pat. No. 3,893,747; Nagel U.S. Pat. No. 3,894,786; Golden et al U.S. Pat. No. 3,894,790; Nagel U.S. Pat. NO. 3,895,855; Nagel U.S. Pat. No. 3,905,680; Nagel U.S. Pat. No. 3,905,681; and the like. Even when prior art reflectors have retroreflective capability through included angles greater than about .+-.30.degree., such are not directly adapted for use in the highway roadside marking field. For one thing, some of such prior art reflectors can have retroreflective characteristics which go so far beyond an included angle of 90.degree. that they become safety hazards in that they could equally guide motorists approaching the same point from opposed directions. For another thing, some of such prior art reflectors, if mounted along a roadside, do not produce continuous retroreflectivity in the range from 0.degree. to 60.degree.; for example, if one endeavours to move a reflector of the type shown in Heenan U.S. Pat. No. 3,332,327 to an elevated position along the side of a road, one still does not obtain continuous retroreflectivity from such a reflector through an angle of from 0.degree. to 60.degree.. In the highway roadside or barrier marker field, reflector constructions specially adapted for positioning and mounting along road side edge portions are needed and necessary in order to permit economical installation, low maintenance costs, long life, good reflectance characteristics over the ranges desired (as above indicated), and the like. New and improved reflector constructions which are specially adapted for this class of application are thus needed.